The present invention is generally directed to data communications completed via a cellular mobile radiotelephone (CMR) system. More particularly described, the present invention supports the communication of increased data content from a mobile station to a data collection system via a mobile switching center (MSC) by utilizing the dialed digits field of CMR signals to carry the data content.
In recent years, the communications industry has shown a growing interest in various types of wireless communications systems for communicating data between a remote site and a central location. It is well recognized that the use of a dedicated telephone facility for a conventional telephone system is not a convenient, economical, or practical option for all communications applications. For example, a home security system may be equipped with a device for transmitting information identifying the home to a monitoring system in the event of a break-in. While a conventional telephone link may be utilized to transmit the identifying information, a clever burglar could easily prevent the identifying information from being sent to the monitoring facility by disconnecting the telephone link outside the home. In view of problems such as these, the communications industry has developed wireless communications systems for communicating data in applications where a conventional telephone link is undesirable. One such system involves the use of a cellular network control channel in a cellular mobile radiotelephone (CMR) system to transport data messages.
While previous data communications systems for communicating a data message via the cellular network control channel of a CMR system are easily implemented because they operate within an industry-standard CMR system, these systems are not without drawbacks. For instance, in some previous systems the data path is achieved by altering the Electronic Serial Number (ESN) field of an Autonomous Registration signal (or Call Origination Signal) to carry data content instead of an identification characteristic. While useful in many business applications, such as security alarms, vehicle or cargo location, meter monitoring, etc., these previous data communications systems are limited by the size of the data that can be transported in the described manner via the cellular network control channel.
Other data communications systems have been developed that support data messaging over a CMR system by issuing a Feature Request message having data content within the dialed digits field. These systems are also not without drawbacks. In some such systems, a special activation code or identifying characteristic, such as an asterisk and/or one or more digits, is recognized by the MSC to enable the communication of data content from a mobile station to a home location register (HLR) system. In this manner, a messaging unit, such as a mobile station, can send data messages via the conventional CMR system by issuing a Feature Request message having encoded data content without use of a voice channel resource of the CMR system. However, at least a portion of the dialed digits field within the Feature Request message must be occupied by the identifying characteristic to support the transmission of the data content within the remaining portion of the dialed digits field. This identifying characteristic allows the use of a dedicated Feature Request message that may be intercepted by the MSC for transmission of encoded data content as a data message. This identifying characteristic creates a serious limitation of these previous systems because it drastically limits the amount of data that may be transmitted by occupying a portion of the space that could otherwise be used to carry data.
Accordingly, in light of the above problems, there is a need for a method and system for adapting an existing communications network to carry an increased data payload. There is a further need to adapt an existing communications network to deliver an increased data payload without the use of an identifying characteristic. There is an additional need for a method of adapting the existing architecture of a CMR system in a efficient and cost-effective manner to support an increased data payload via the CMR system. This new use of an existing communications network should have a minimum impact upon present communications carried by the system.
The present invention solves the problems described above by providing a method and system for expanding the data payload of data messages transported via a cellular network control channel. The present invention can advantageously use one or more call processing triggers at the mobile switching center (MSC) to substitute an IS41 Origination Request message carrying data content for the more typical Qualification Request message in connection with a mobile station having Per Call authorization. This substitution of the Origination Request message permits placement within the dialed digits field of data content, obtained from the Call Origination signal received at the MSC, for forwarding to the distant home location register (HLR) system associated with the mobile station. Significantly, the dialed digits field can be advantageously modified to contain only a data payload rather than the combination of data and an identifying characteristic that identifies data content within the dialed digits field.
More particularly described, the present invention supports data communication via the cellular mobile radiotelephone (CMR) system by the use of the dialed digits field within certain standard CMR system-compatible signals. Prior to data communication operations, a mobile station can issue an IS553 Autonomous Registration signal via the cellular network overhead control channel for processing by the MSC that serves the cell in which the mobile station is operational. This results in the transmission of an IS41 Registration Notification message to the HLR system that is associated with the mobile station. The HLR system can respond to the Registration Notification message by generating an Registration Notification RETURN RESULT having an Authorization Period field set to Per Call status. The visitor location register (VLR) system will construct a database entry in response to this Registration Notification RETURN RESULT, thereby causing the MSC to transmit subsequent IS41-compatible messages to the HLR system associated with the mobile station prior to any actual call delivery attempt. By setting one or more appropriate call processing triggers at the MSC, the switch can transmit an IS41 Origination Request message rather than the conventional IS41 Qualification Request message to the HLR system. In this manner, the MSC is programmed to seek authorization for any subsequent call origination by that mobile station based upon the use of an IS41 Origination Request message rather than the more conventional Qualification Request message. The trigger event for this message replacement can be set at the MSC prior to any communication of data content by the mobile station to a data collection system, typically hosted by the HLR system for that mobile station.
In response to a subsequent Call Origination signal by the mobile station, the MSC generates an IS41 Origination Request query to its VLR, which results in the forwarding of an Origination Request message to the HLR for that mobile station. Significantly, the Call Origination signal can contain data content within the dialed digits field of that IS553-compatible signal. Likewise, the dialed digits field of the IS41-compatible Origination Request signal contains this data content. The combination of the Call Origination signal and the Origination Request message, carried via the CMR system, results in the communication of data content as encoded information within those signals. Significantly, the entire dialed digits field of these CMR signals can be used to carry data content because the switch has previously been set up to communicate this data content to the HLR system associated within the originating mobile station.
The data payload in a modified Electronic Serial Number (ESN) field and the modified dialed digits field of the CMR signals utilized by the present invention can be combined to increase the data payload of a data message carried by a data communication system. In the alternative, the ESN field can be left unmodified, thereby leaving only the dialed digits field to carry a data payload within an Origination Request message in the manner described above.
The present invention achieves an increase in the data payload capacity for the data message. The present invention can forward up to 32 binary coded decimal (BCD) digits within the dialed digits field of an IS553 Call Origination signal to a mobile switching center (MSC). The MSC responds by transmitting an IS41 Origination Request message containing the encoded data to a data collection system implemented by a distant gateway, such as a home location register (HLR) system associated with the mobile station. The present invention can add to or substitute for the data payload capability of the data communications system utilizing the cellular network control channel to carry data by substituting data content for the entire dialed digits field of an IS553 Call Origination signal and causing an IS41 Origination Request message to forward that data to the distant gateway. The present invention does not need to use an identifying characteristic within the data stored in the dialed digits field to trigger a forwarding of the data payload via a Feature Request message. Consequently, the present invention increases the available data payload size by not consuming a portion of dialed digits field with an identifying characteristic that identifies data content, typically a xe2x80x9c*xe2x80x9d character and, in some cases, additional digits.
In this manner, the present invention advantageously provides a method and system for expanding the data payload of data messages transported via a cellular network control channel. That the present invention improves over the drawbacks of the prior art and accomplishes the objects of the invention will become apparent from the detailed description of the illustrative embodiment to follow.